Past knowledge is gathered, analyzed and documented for the purposes of applying, preserving and succeeding in desired future actions. The more complex the knowledge is the more complex it gets to master it.
The chain of obtaining knowledge has been broken many times and will be broken again and again.
They key is having sufficient detailed mastery of useful key elements of a system that is complete. If you don't have it, anything can go wrong at anytime!
The book Krav Maga - Use Your Body as a Weapon will walk you through the complexity of the most efficient hand-to-hand fighting training system and the intensive steps to master it. Pure Krav Maga - Self Defense Mastery DVD set is an invaluable tool for self study as well that complements the book!
The Author is the third in lineage Israel Defense Force Krav Maga Chief Instructor in the Fighting Fit Academy certifying Israel Defense Force Krav Maga Instructors. His follow up civilian 15 year career as a certified public accountant in auditing of large investment partnerships contributed to the documentation of such a complex but quick and intensive training system.